As thrust cylindrical roller bearings each including a cage which can be produced at low costs by the application of press-cutting process and bending process to a single sheet of metal, techniques described in Patent Document Nos. 1 to 5 are known. FIGS. 15 to 18 show a conventionally constructed thrust cylindrical roller bearing 1 as a first example. This thrust cylindrical roller bearing 1 includes a single cage 2 and a plurality of cylindrical rollers 8, 8. This cage 2 is such as to be produced integrally by bending a metallic plate such as sheet steel and includes a cylindrical inside diameter side rim portion 4, a cylindrical outside diameter side rim portion 5, an intermediate plate portion 6 and a plurality of pockets 7, 7.
Among these, the inside diameter side rim portion 4 is such as to lie in an inner circumferential edge portion of the cage 2 and is formed into an annular shape which continues along the full circumference thereof. In addition, the outside diameter side rim portion 5 is such as to lie in an outer circumferential edge portion of the cage 2 and is formed into an annular shape which is concentric with the inside diameter side rim portion 4 and which continues along the full circumference thereof. In addition, the intermediate plate portion 6 is such as to lie between the inside diameter side rim portion 4 and the outside diameter side rim portion 5 and has a cross section which is bent in the radial direction. Furthermore, the individual pockets 7, 7 are such as to be formed in the intermediate plate portion 6 in such a manner as to be each oriented in a radial direction and arranged intermittently with respect to a circumferential direction of the intermediate plate portion 6, and the cylindrical rollers 8, 8 are individually rotatably held in the pockets 7, 7.
As is shown in FIG. 16, a central flat surface 9 which expands in a direction which is at right angles to a revolution center axis of each of the cylindrical rollers 8, 8 and chamfered portions 11 each having a partially circular coned convex surface shape or a convexly curved surface shape whose cross section is formed into a partially convex arc shape are formed on both axial end faces of each of the cylindrical rollers 8, 8. In the case of the conventional construction, of dimensions of the chamfered portion 11, a dimension L8 in an axial direction of the cylindrical roller 8 and a dimension W8 in a radial direction thereof are made substantially equal (L8≈W8). In addition, portions on the intermediate plate portion 6 which lie between the pockets 7, 7 which are adjacent to each other in the circumferential direction make up pillar portions 12, 12.
In addition, the intermediate plate portion 6 is made up of a central flat plate portion 13, an outer diameter side flat plate portion 14, an inside diameter side flat plate portion 15, an inside diameter side connecting portion 16, and an outside diameter side connecting portion 17. Among these, the central flat plate portion 13 is formed at a portion of the intermediate plate portion 6 which lies radially (horizontally in FIGS. 15, 17, vertically in FIG. 18, and in a direction from near to far side or vice versa in FIG. 19) middle and axially closer to one end (a lower end in FIGS. 15, 17) thereof. In addition, the outside diameter side flat plate portion 14 is formed at a portion of the intermediate plate portion 6 which lies adjacent to a radially inside (a left side in FIG. 17) of the outside diameter side rim portion 5 and axially closer to the other end (an upper end in FIGS. 15, 17) thereof. The outside diameter side and inside diameter side flat plate portions 14, 15 are situated on the same plane. In addition, the inside diameter side connecting portion 16 connects an outer circumferential edge of the inside diameter side flat plate portion 15 with an inner circumferential edge of the central flat plate portion 13, and the outside diameter side connecting portion 17 connects an outer circumferential edge of the central flat plate portion 13 with an inner circumferential edge of the outside diameter side flat plate portion 14. A space between the inside diameter side and outside diameter side connecting portions 16, 17 increases as it goes farther away from the central flat plate portion 13. An external side surface of the central flat plate portion 13 and distal end edges of both the inside diameter side and outside diameter side rim portions 4, 5 are situated on the same plane, or the external side surface of the central flat plate portion 13 projects axially further than the distal end edges.
The cage 2 that is configured as has been described above is disposed between a pair of planes 40a, 41a, axially opposite and parallel to each other, which constitute raceway surfaces of a pair of members which make up the thrust cylindrical roller bearing in such a state that the cylindrical rollers 8, 8 are rotatably held in the pockets 7, 7, individually. Of the central, outside diameter side and inside diameter side flat plate portions 13 to 15 which make up the intermediate plate portion 6, portions which constitute both circumferential side edges of the pillar portions 12, 12 project slightly further inwards into the pockets 7, 7 than both the inside diameter side and outside diameter side connecting portions 16, 17.
Namely, of the outside diameter side flat plate portion which is positioned outwards in a diameter direction and the inside diameter side flat plate portion 15 which is positioned inwards in a diameter direction, portions which constitute circumferential end edge portions of the pillar portions 12, 12 are made to constitute outside diameter side locking portions 18, 18 and inside diameter side locking portions 19, 19, respectively. Then, as is shown in FIGS. 17(a) and 19(a), an axial displacement of the cage 2 to an axial end side (a lower side in FIGS. 17, 19) is controlled by the engagement of the outside diameter side and inside diameter side locking portions 18, 19 with a rolling surface 10 of each cylindrical roller 8 so that part of each cylindrical roller 8 is left projecting axially further than the distal end edges of the central plate portion 13 and both the inside diameter side and outside diameter side rim portions 4, 5.
In addition, of the central flat plate portion 13 which is positioned intermediate in a diameter direction, portions which constitute the circumferential end edge portions of the pillar portions 12, 12 are made to be central locking portions 20, 20, respectively. The, as is shown in FIGS. 17(b) and 19(b), an axial displacement of the cage 2 to the axial end side (an upper side in FIGS. 17, 19) is controlled by the engagement of the central locking portions 20, 20 with the rolling surface 10 of each cylindrical roller 8 so that part of each cylindrical roller 8 is left projecting axially further than both the outside diameter side and inside diameter side flat plate portions 14, 15.
In short, the axial displacement of the cage 2 relative to the cylindrical rollers 8, 8 is suppressed by bringing the respective locking portions 18 to 20 into engagement with the rolling surfaces 10 of the cylindrical rollers 8, 8 in such a state that the cylindrical rollers 8, 8 are held in the pockets 7, 7, respectively. Namely, the positioning of the cage 2 relative to the axial direction is realized by the so-called roller guide.
As the cylindrical rollers 8, 8 which constitute the thrust cylindrical roller bearing that has been described above, as is shown in FIG. 16, which has been described above, more cylindrical rollers in which central portions (portions inwards of chamfered portions which lie closer to an outer circumferential edge) of both axial end faces are made into flat surfaces have come to be used in recent years with a view to securing a load-carrying capacity. Namely, although among cylindrical rollers, there are some cylindrical rollers of which both axial end faces are formed into a partially spherical surface or a convex surface which is made up of a circular cone-shaped surface, in the case of these cylindrical rollers, the axial length (the effective length) of the rolling surface which can bear a load becomes short, and a load that can be borne by the rolling surface becomes small by such an extent. In contrast to this, with the cylindrical rollers 8, 8 in which the central portions of both the axial end faces are made into the flat surfaces, the effective length L (refer to FIG. 16) is secured, the securing of load-carrying capacity of the thrust cylindrical roller bearing 1 in which the cylindrical rollers 8, 8 is facilitated.
Incidentally, when the thrust cylindrical roller bearing that has been described above is in use, a force is exerted on the individual cylindrical rollers 8, 8 which is directed outwardly in a diameter direction. Then, of both the axial end faces of each of the cylindrical rollers 8, 8, the outside diameter side end face 21 which is situated in a diameter direction outer side of the cage 2 is pressed against, of circumferential edge portions of each of the pockets 7, 7, an outside diameter side circumferential edge portion 22 which is situated in the diameter direction outer side of the cage 2. As a result of this, the outside diameter side circumferential edge portion 22 and the outside diameter side end face 21 are caused to rub against each other at a portion shaded with lattice pattern in FIG. 19(a). However, it is not that this outside diameter side end face 21 is pressed against the outside diameter side circumferential edge portion 22 uniformly. In the real world, the outside diameter side end face 21 and the outside diameter side circumferential edge portion 22 are brought into sliding contact in such a state that a portion of the outside diameter side end face 21 which lies closer to the outside diameter side thereof is pressed against the outside diameter side circumferential edge portion 22 due to the cylindrical rollers 8, 8 skewing in the pockets 7, 7.
Namely, while the thrust cylindrical roller bearing 1 is in operation, although it is ideal that the direction of the revolving axis of the cylindrical rollers 8, 8 and the diameter direction of the cage 2 coincide with each other, in the real world, it is not possible to avoid the occurrence of skewing which causes a case where those directions do not coincide with each other. Skewing like this occurs because a frictional coefficient at rolling contact portions between the rolling surfaces 10 of the cylindrical rollers 8, 8 and the raceway surfaces is not uniform relative to a length direction of the rolling contact portions. In addition, an extent to which the outside diameter side end face 21 and the outside diameter side edge portion 22 are brought into offset collision becomes remarkable as a deviation angle (a skew angle) between the two directions increases.
In the event that a boundary portion between an outer circumferential edge portion of the central flat surface 9 and the chamfered portion 11 on the outside diameter side end face 21 and the outside diameter side circumferential edge portion 22 are caused to rub against each other while the cylindrical rollers 8, 8 are skewing, a local concentration of stress occurs at the portion where the rubbing is occurring, and moreover, the boundary portion and the outside diameter side circumferential edge portion 22 are caused to rub against each other at fast rubbing speed. Furthermore, an oil film for lubrication becomes difficult to be formed at this mutual rubbing portion, and a metal contact becomes easy to occur at the mutual rubbing portion. As a result of this, a concavely recessed portion 23, in which the degree of wear becomes remarkable on both sides in the circumferential direction of the cage 2 as is shown in FIG. 20, is formed on the outside diameter side circumferential edge portion 22 in part of the cage 2 which is made of a soft metal compared to a bearing steel of which the cylindrical rollers 8, 8 are made.
When the convexly recessed portion 23 so formed becomes large to some extent, so-called drilling wear occurs in which the chamfered portion 11 which is provided on the outer circumferential edge of part of each of the cylindrical rollers 8, 8 which faces in a diameter direction outer end portion of the cage 2 enters the interior of the concavely recessed portion 23 to thereby be displaced further outwards in the diameter direction of the cage 2 than the position of each of the pockets 7, 7. In the event that drilling wear like this occurs, the sliding resistance of the roller end face relative to the cage is increased, which increases the rotational resistance of the rotary supporting portion in which the thrust cylindrical roller bearing is built, whereby not only the performances of various mechanical apparatuses which have such rotary supporting portions are decreased but also in the event that that the increase in rotational resistance becomes remarkable, it causes a failure such as flaking and seizing. Wear which causes these drawbacks has become easy to occur as the revolution speeds of rotary portions of various mechanical apparatuses such as transmissions and automotive air conditioners are increased by the increase in performance of motor vehicles in these years.
On the other hand, in a case where a cylindrical roller 8a in which both axial end faces are made into a partially spherical convex surface as is shown in FIG. 21 is installed, as is shown in FIG. 22, in a cage 2 which has a similar construction to the conventional construction that has been described heretofore, whether or not skewing occurs, an end edge of an internal surface of an outer diameter side circumferential edge portion 22 of a pocket 7 in the cage 2 and an outside diameter side end face 21a of the cylindrical roller 8a which is formed into the partially spherical convex surface are caused to rub against each other (brought into edge collision with each other), whereby a partially arc-shaped concavely recessed portion 23a shown in FIG. 23 is formed in a central portion of the outside diameter side circumferential edge portion 22. Then, when this concavely recessed portion 23a becomes large, a problem like the one described above is also caused.
A construction described in Patent Document No. 5 has conventionally been known as a construction which reduces the drawback that has been described above. FIG. 24 shows a related art construction which follows an invention described in Patent Document No. 5. In the case of this related art construction, a pocket 7a in a cage 2 is formed to such an extent that it reaches a proximal portion of an outside diameter side rim portion 5a. In addition, a cylindrical roller 8, in which both axial end faces are formed into a partially spherical convex surface is retained within the pocket 7a, and the outside diameter side end face 21a of the cylindrical roller 8a is made to face an inner circumferential surface of the outside diameter side rim portion 5a. In the case of the related art construction which is constructed as has been described above, even in the event that both the surfaces are caused to rub against each other, since a diameter of the mutual rubbing portion is made small to thereby suppress the rubbing speed V to an extremely low level, the wear of the mutual rubbing portion is suppressed. In the case of the related art construction described in the cited document No. 5, since the cylindrical roller 8a in which the axial end faces are formed into the convex surface needs to be used, of this cylindrical roller 8a, the axial length L a of the rolling surface which can bear the load becomes short, and the load that can be borne becomes small by such an extent.
Patent Document No. 1: JP-A-6-94038
Patent Document No. 2: JP-A-2000-213546
Patent Document No. 3: JP-A-2002-206525
Patent Document No. 4: JP-A-11-351245
Patent Document No. 5: JP-A-2003-83333